1. Field of the Invention
The present invention relates to ballast control for a fluorescent lamp and, more particularly, to a lamp ballast circuit and method.
2. Description of the Related Art
A semiconductor device for ballast control of a fluorescent lamp is typically designed to drive a power switch implemented as a metal-oxide semiconductor field-effect transistor (MOSFET). A MOSFET is turned on (or driven) by the application of an appropriate voltage at its gate electrode. When the MOSFET element is turned on, no current flows to the gate electrode and no power is consumed. In order to drive a bipolar junction transistor (BJT), however, not only must an appropriate voltage be applied between the base and the emitter of the BJT to turn it one, but a continuous base driving current is needed to maintain the on state after the BJT is turned on. Accordingly, a driving circuit for a BJT-implemented power element must supply a base current while also providing the necessary voltage difference between the base and emitter to turn on the BJT. Therefore, with a BJT-implemented power element, more power is consumed and more heat is generated by the driving circuit than would be the case for a MOSFET-implemented power element.
But a BJT-implemented power element is cheaper than a MOSFET-implemented power element. Thus, the cost of a fluorescent lamp ballast can be reduced if an efficient method for driving a BJT-implemented power element is provided.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.